Poly metal radical” approach

Finally, according to basic equilibrium principles, additional Co favors recombination with propagating radicals. Consequently, in spite of the low propensity of Co(acac)2 to deactivate poly(acrylate) radicals, the successful controlled polymerization of acrylates was demonstrated when using a substantial excess of Co(acac)2 [30]. The drawback of this approach, however, was an ampHfied contamination of the final material by the metal. 

The active center may be a free-radical, ion. or metal-carbon bond (Chapter 6). In any event the propagating species 4-6 will be more stable than its counterpart 4-7 if the unpaired electron or ionic charge can be delocalized across either or both substituents X and Y. When X and/or Y is bulky there will be more steric hindrance to approach of the two substituted C atoms than in attack of the active center on the methylene C as in reaction (4-1). Poly(vinyl lluoride) contains some head-to-head linkages because the F atoms are relatively small and do not contribute significantly to the resonance stabilization of the growing macroradical. 

Our work employs electrochemically initiated polymerization (EIP) which is an easy and flexible method to produce surface coatings of various kinds. The technique makes use of the decomposition of an electro-active initiator at an electrode to start a free-radical polymerization. The polymer is formed directly at the electrode surface. As a consequence, the films adhere tightly to the surface. Adhesion is based on physisorption of the hydrogel to the metal. Note in this context that EIP is different from electrografting of conductive polymers. In EIP, the initiator is the electro-active species, rather than the monomer. Recently, we reported on the formation of thermoresponsive poly-A -isopropylacrylamide (pNIPAm) hydrogel coatings on gold surfaces based on this approach. ... 

However, all synthetic approaches involving ATRP rely on a metal catalyst. Full metal-free and thus greener approaches to block copolymers were realized by the combination of Upase ROP with nitroxide-mediated living free radical polymerization [44]. With this system it was also possible to successfully perform a one-pot chemoenzymatic cascade polymerization from a mixture containing a dual initiator, CL and styrene (Fig. 12). Moreover, it was shown that this approach is compatible with the stereoselective polymerization of 4-methylcaprolactone for the synthesis of chiral block copolymers. A metal-free synthesis of block copolymers using a radical chain transfer agent as a dual initiator in enzymatic ROP to yield poly(CL-f -styrene) was also reported recently [119]. 

Simple nonfunctional hydrocarbon polymers such as polyethylene (PE), polypropylene, poly-a-olefins and their copolymers are synthesized by uncontrolled high-pressure-high-temperature radical, metathesis or transition-metal-catalyzed coordination polymerization (Natta, 1956 Ziegler et al, 1955 Wu and Grubbs, 1994 Chanda and Roy, 1993). Although catalysts of exceptional efficiency that produce polymers on a huge scale are in common use, control that approaches a hving polymerization for these methods has not been realized. 

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